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Old 05-05-2010, 05:18 AM
Douglas McClendon
 
Default Snapshot handover working, yippee!, was semop failed for cookie?

Ok, so my complaining about code-progress should now be complete. I
think I'm back in action. But the "BUG: lock held when returning to
user space" still seems like a message you folks wanted yourselves to hear.


After grumbling to myself that fedora doesn't provide a package with
dmsetup.static, I went ahead and copied all relocatable deps
(/lib/ld-linux.so.2??) to tmpfs along with dmsetup, using
LD_LIBRARY_PATH. I also used --noudevrules and --noudevsync. Then I
followed the documentation I found which, for use cases as esoteric as
mine, might be desirable in snapshot.txt


https://patchwork.kernel.org/patch/59806/

I.e. rules for snapshot handover in the general case. (who knows, maybe
I'll be the only user of non-snapshot-merge snapshot handover for all
time) (though technically I guess you can call what I've been doing for
the last several years to be an alternate form of snapshot merging.
I.e. where your snapshot base is readonly and you are merging both the
readonly base and cow to a third writable device)


Anyway, I finally got my stuffs working again, or at least, I have a
virtual snapshot-as-rootfs being dm-mirror migrated right now. I assume
that my loading of a new table, is sufficiently equivalent to the
dmsetup remove of the old snapshot as described in the above link.


But finally, and the real reason for this message- during this I noticed
that the aforementioned "BUG:" was not in fact what was killing my
system. I.e. I still get that message, though everything else appears
to work and it appears to be harmless (I hope).


BUG: lock held when returning to user space!

dmsetup/865 is leaving the kernel with locks still held!
1 lock held by dmsetup/865:
#0: (&journal->j_barrier){+.+...+}, at: [<c056b84d>] jbd2_journal_lock_
updates+0xbd/0xc5

Thanks again for putting up with my corner case complaints.

Cheers,

-dmc

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Old 05-05-2010, 03:22 PM
Mike Snitzer
 
Default Snapshot handover working, yippee!, was semop failed for cookie?

On Wed, May 05 2010 at 1:18am -0400,
Douglas McClendon <dmc.fedora@filteredperception.org> wrote:

> Ok, so my complaining about code-progress should now be complete. I
> think I'm back in action. But the "BUG: lock held when returning to
> user space" still seems like a message you folks wanted yourselves
> to hear.
>
> After grumbling to myself that fedora doesn't provide a package with
> dmsetup.static, I went ahead and copied all relocatable deps
> (/lib/ld-linux.so.2??) to tmpfs along with dmsetup, using
> LD_LIBRARY_PATH. I also used --noudevrules and --noudevsync. Then
> I followed the documentation I found which, for use cases as
> esoteric as mine, might be desirable in snapshot.txt
>
> https://patchwork.kernel.org/patch/59806/
>
> I.e. rules for snapshot handover in the general case. (who knows,
> maybe I'll be the only user of non-snapshot-merge snapshot handover
> for all time) (though technically I guess you can call what I've
> been doing for the last several years to be an alternate form of
> snapshot merging. I.e. where your snapshot base is readonly and you
> are merging both the readonly base and cow to a third writable
> device)
>
> Anyway, I finally got my stuffs working again, or at least, I have a
> virtual snapshot-as-rootfs being dm-mirror migrated right now. I
> assume that my loading of a new table, is sufficiently equivalent to
> the dmsetup remove of the old snapshot as described in the above
> link.

Glad to hear snapshot cow handover is working well for you.

> But finally, and the real reason for this message- during this I
> noticed that the aforementioned "BUG:" was not in fact what was
> killing my system. I.e. I still get that message, though everything
> else appears to work and it appears to be harmless (I hope).
>
> BUG: lock held when returning to user space!
>
> dmsetup/865 is leaving the kernel with locks still held!
> 1 lock held by dmsetup/865:
> #0: (&journal->j_barrier){+.+...+}, at: [<c056b84d>] jbd2_journal_lock_updates+0xbd/0xc5

This is an ext4 issue that has been fixed upstream, see:
https://bugzilla.redhat.com/show_bug.cgi?id=568503

and it is staged for inclussion in the next kernel (2.6.35):
http://git.kernel.org/?p=linux/kernel/git/tytso/ext4.git;a=commit;h=74a8f0090293696a716c728f9cd484 b45083937f

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